Transcript Slide 1

Control & Automation
For
Super Critical Units
K.S. Sundaram
NTPC, SIPAT
1
Introduction
•
Requirements
•
Comparison of Auto loops -Sub Critical Vs Super Critical
•
Feed Water Control
•
Steam Temperature Control
•
Unit Control
•
Turbine Control
• Discussions
2
Super Critical Units
•
Increased requirement of accuracy and resolution of DDCMIS
systems.
•
•
•
No drum, hence no energy reserve.
•
Smooth changeovers between wet to dry operation and vice
versa
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•
Control system should ensure smooth steady state operation.
Need to match fuel ,air and feed water accurately.
Stringent requirement of temperature controls as unbalance in
fuel and feed water has significant change in temperatures.
Little need for operator intervention.
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4
Source :KEPRI
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Source :KEPRI
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Source :KEPRI
Comparsion Of Major Loops
Name of the loop
Remarks
SIPAT 660 MW
Furnace Draft
No major difference
Blade pitch control, Hydraulic
Air flow control
No major difference
Blade pitch control, Hydraulic
PA Hdr. control
No major difference
Blade pitch control, Hydraulic
Fuel master
Cross limiting from FW
VFD in feeders
FW control
Saturation Temp Controller
TDBFP 2 X 65%,
MDBFP 2X30%
SH temp control
FW plays a major role
FW plays a major role (Trip at
Temp >565 Deg)
RH temp control
No major difference .
Spray Should be Zero
Two tilts per corner (Trip at
Temp>580 Deg)
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List Of Loops For Discussion
S.N. Name of the loop
Sub loops
01
Feed Water control
Feed Water Master
BCP / UG valve
FWPCV control
Separator Drains control
02
Super heater temp
control
Platen SH temp control
SH steam temp control
03
RH steam temp
control
Burner tilt control
Spray valves control
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Feed Water Control Requirements
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•
Ensure feed water flow in relation to unit demand.
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Ensure the rangeability of platen SH spray valves
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Ensure protection for Fuel /FW ratio.
Adjust feed water flow to get the desired separator outlet
temperature and degree of super heat.
Incorporate the start up level demand.
Ensure minimum required feed water flow.
Convert the flow requirement into pump demand with
compensation for pump capacities.
Ensure the pumps are within the operating range.
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Final Control Elements In FW Loop
Control Element
MDBFP
SCOOP/TDBFP
Speed
BC Pump
Discharge Valve
Initial Condition Till
Chemical Parameter Is
Achieved Before
BC Pump Start
Condition From BC
Pump Start / BLU
Up To Load < 30 %
WET MODE
Load > 30 %
DRY MODE
FW master in manual
control. Initial FW flow
at 200 T/Hr and
Later 600T/Hr when
WR opens to 30%
Separator
Level control
Feed water flow
control
Feed water flow
control
--
--
Feed water
Valve ( Eq. to
30% Valve )
FW pressure control at
upstream of valve
FW pressure
control at
upstream of valve
Full open and
bypass valve opens
Separator Drain
Valves WR/ZR
Separator
Level control
Separator Hi
Level
--
10
Feed Water Master In Wet Mode
ACTUAL LEVEL
SEPARATOR LEVEL SETPOINT
SUB
10
PID
LEVEL SETPOINT
SEPARATOR
LEVEL SET
POINT FROM
ULD
8
6
Series1
4
2
0
0
100
200
300
400
ULD
TO BFPS
ULD
SP
0
9
300
3
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Min FW Flow Control In Wet Mode
MIN. FW FLOW
SET POINT
FW FLOW TO
ECONOMISER
SUB
DP ACROSS BC
PUMP
PID
DP SET POINT
ACROSS BC
PUMP
SUB
PID
<
BC PUMP WILL TRIP IF DP
UG VALVE
IS < 4.5 Kg/Sqcm
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FWPCV Valve Control In Wet Mode
BFP HEADER
PRESSURE
TRANSMITTERS
SEL
HIGHEST OF TDBFP
SUCTION FLOWS
SUB
HIGHEST OF MDBFP
SUCTION FLOWS
FG
FG
>
PID
FWPCV
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Separator Drains Control
MEASURED SEPERATOR LEVEL
F(X)
WR
F(X)
ZR
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Wet Mode Operation
• Separator level control by BFPs and FW flow control by UG .Min FW
flow set point from boiler desk. Initial level set point is 9 Mtr. WR and
ZR will act as emergency control for separator level
• If water disappears in separator during wet mode then boiler will trip
on separator level low low – 1.1 Mtr (3 Sec delay)
• Boiler will trip if separator outlet level goes high high in wet mode –
17.7 Mtr
• WR opens at 14.2 Mtr in auto
• ZR opens at 16.2 Mtr in auto
•
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Wet Mode & Dry Mode Of Operation
Source: Doosan
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Feed Water Control In Dry Mode
• First controller acts on load dependant average DT across PDSH.
Its output represents the required adjustment to maintain the steam
conditions, flue gas temperatures entering Platen SH so as to
ensure adequate spray platen range.
• Second
controller acts on load dependant separator temperature
set point corrected by first controller. The output adjusts feed water
in response to firing system disturbances.
• Minimum set point of 30% for safety is additionally provided.
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FW Master In DRY Mode
BMD
SEPERATOR
OUT STM TEMP
PLATEN SH DT
BOILER MASTER
DEMAND
DSH
SEPERATOR OUTLET
TEMP SET POINT
SEP
F2(x)
F1(x)
PI
FG
NOT DRY MODE
SET TO ZERO
∑
PI
FF SIGNAL
∑
ANY SCANNER FLAME
(AND) BCP OFF
0%
A
a
>
TOTAL FW FLOW
FWF
F(x)
T2
b
30 %
A
FB SIGNAL
PI
Source : KEPRI
TO BFPs
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Platen DSH DT Set Point
DT SETPOINT IN FW LOOP
DT SETPOINT
30
25
20
15
Series1
10
5
0
0
50
BOILER MASTER
100
BM(%)
DT
0
28.8
43.3
52.1
70.7
91
100
0
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22
9
9
11
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Source : EMERSON
Source : EMERSON
Source : EMERSON
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Runbacks /Rundowns/Protections
Runbacks /Rundowns
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Two TDBFPs – 120%
One TDBFP + One MDBFP – 95%
One TDBFP – 65%
One MDBFP – 30%
Rundown if FW deviation is high
BFPS will go for pressure control when FW deviation is very high
ID / FD / PA runback demand is 396 MW and turbine trip is 330 MW
Protections
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Feed water flow low low for 10 sec ( 440 T/Hr)
Vertical wall tube metal temperature Hi Hi (4/48) (479 Deg)
MS / RH STEAM temperature Hi Hi 565/580 Deg
All BFP off for 20 Sec

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Platen SH Temperature Control
• DT
across PDSH is taken care by Feed water control.
• DT across FDSH and Load dependant DT SP acts on master
with over/ under firing FF which is derived from comparing rate of
change of fuel flow to rate of change of steam flow.
• Master output goes to slave via SP correction from steam flow
where input is PDSH outlet with saturation temp limitation.
• Incase of start up only master controller will be in service.
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Final DSH DT Set Point
DT SETPOINT FOR FDSH
DT SETPOINT
30
25
20
15
Series1
10
5
0
0
50
BOILER MASTER
100
BM(%)
DT
0
28.8
43.3
52.1
70.7
91
100
0
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21
18
7
7
7
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SH Temperature Profile
DIV SH
406
451
PLATEN SH
440
FINAL SH
480
486
DSH1
15%
540
DSH2
3%
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Source : KEPRI
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Final SH Temperature Control
• DT
across FDSH is taken care by Platen SH temperature control.
• Final SH O/L temp and Load dependant temp SP acts on master
with over/under firing FF which is derived from comparing rate of
change of fuel flow to rate of change of steam flow.
• Master
output goes to slave via SP correction from steam flow
where input is FDSH outlet with saturation temp limitation.
• Incase of start up only master controller will be in service.
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Source : KEPRI
29
RH Temperature Control (Tilt)
RH O/L AVG temp and temp SP (568 DEG) with
RHDSH DT
correction (Max 5 DEG) correction fed to
PID, PID output with airflow FF goes to 2 sets of tilt - one
for wind box and other for SOFA
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Source : KEPRI
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RH Temperature Control By Spray
• RH
O/L temp and load dependant temp. SP acts on master
controller.
• Master
controller output is corrected with over/ under firing FF
which is derived from comparing rate of change of fuel flow to rate
of change of steam flow.
• Master O/P goes to slave via SP correction from steam flow where
input is RHDSH outlet with saturation temp. limitation.
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Source : KEPRI
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Source :KEPRI
Source : EMERSON
Source : EMERSON
Turbine Control
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Speed Loop- Till synchronization (IP Rolling)
IP is Throttle governing & HP is Nozzle governing
Open load loop till HP is charged
Pressure Control when HP is charged
Sliding Pressure Operation from 90 to 247 Kg/sqcm
Achieve full load & put on CMC
Salient Features:
• Individual EHC for individual valves
• No Hydraulic back up operation
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HP BP Control
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LPBP Control
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References
• KEPRI logics
• EMERSON Logics
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THANK YOU
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FEED WATER PATH INITIAL STAGE
Back
VERTICAL WW
SEPARATORS
F
W
R
S
STORAGE TANK
ECONOMISER
ECO I/L
W
R
F
L
A
S
H
T
A
N
K
HPH
ZR
CONDE
NSER
CEP
LPH
DA
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Back
FEED WATER PATH - LOAD < 30%
VERTICAL WW
SEPARATORS
S
T
O
R
A
G
E
T
A
N
K
HPH
ECONOMISER
ECO I/L
MIXING PIECE
BCP
UG
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Back
FEED WATER PATH – LOAD > 30%
S
E
P
A
R
A
T
O
R
S
E
P
A
R
A
T
O
R
VERTICAL WW
HPH
ECONOMISER
ECO I/L
TO BACKPASS
CONNECTING PIPES
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CCP Auto Start And Auto Stop Conditions
Source :Doosan
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